Religious music serves as the backdrop for bestseller Penny’s excellent eighth novel featuring Chief Insp. Armand Gamache of the Quebec Sûreté (after 2011’s A Trick of the Light). Gamache and his loyal number two, Insp. Jean-Guy Beauvoir, travel to the isolated monastery of Saint-Gilbert-Entre-les-Loups, which produced a CD of Gregorian chants that became a surprise smash hit, to investigate the murder of its choirmaster, Frère Mathieu, found within an enclosed garden in a fetal position with his head bashed in. Gamache soon finds serious divisions among the outwardly unified and placid monks, and begins to encourage confidences among them as a first step to catching the killer. Traditional mystery fans can look forward to a captivating whodunit plot, a clever fair-play clue concealed in plain view, and the deft use of humor to lighten the story’s dark patches. On a deeper level, the crime provides a means for Penny’s unusually empathic, all-too-fallible lead to unearth truths about human passions and weaknesses while avoiding simple answers. 150,000 first printing; author tour. Agent: Patty Moosbrugger, Teresa Chris Literary Agency. (Aug.)